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What would it be like to be on an inhabitable (presumably terraformed) world of an O star?
I am thinking a brilliant deep purple sky, like the light of a UV lamp, and shadow bands from the star "twinkling" looking like the sunlight on the floor of an outdoor swimming pool. The star is a blue pinpoint. Shadows are razor sharp. Probably look ghastly.
Am I close? Any other observations?
SHARKS (crossed out) MONGEESE (sic) WITH FRICKIN' LASER BEAMS ATTACHED TO THEIR HEADS
Order of Kilopi
I don't think you'd see shadow bands. Plugging in values for an O3V from Lang's venerable tables (52500K, 15 solar radii), I get an apparent diameter, when irradiance equals Earth's, of 21 seconds of arc. That's equivalent to Mars or Saturn at closest approach to Earth, and they don't twinkle. No twinkle, no shadow bands.
Illumination would be low compared to Earth (about 2%), but not so's you'd notice--that's about what you get from operating table lights. The predominance of short wavelengths (as compared to the Sun's relatively flat spectral distribution) would compensate for that somewhat, in terms of blue and violet scattering, but the sky would actually be less bright than Earth's (ceteris paribus), just because it's less well illuminated. But again, not noticeably so. Our eyes are less sensitive to violet than to blue, so the additional violet wavelengths wouldn't necessarily make a huge difference--we're maybe talking lilac or periwinkle blue rather than sky blue. (Certainly not purple, which would require a red admixture.)
The surface brightness of such a star is huge (I get 2.6x1011cd.m-2 - ten times the flash from an atomic bomb, and a hundred times that of the solar disc), but we can reduce that by a factor of ten because of the diffraction limitation of the human eye. If stories about atomic bomb flashes causing retinal damage before a person can blink are true, then the stellar disc might be a significant hazard to vision. It certainly seems likely you'd develop photic retinopathy much faster, given the higher surface brightness and higher UV content.
Grant Hutchison
Order of Kilopi
If its terraformed - that is, modified to support Earth life - there would need to be an optical filter between the surface and the sunlight, or the UV will kill everything. I doubt a wisp of ozone would be sufficient. Probably an in-space disk filter would be preferable between the planet and the star. The filter could also be made to block some of the visible light, which might make it nicer for humans and other species.
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The Leif Ericson Cruiser
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Originally Posted by grant hutchison
Only that? I would have thought to have sufficient light to be equivalent to what the Earth receives in optical (for terraforming) that the UV would be far more intense than just causing relatively minor issues like quicker eye damage.
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The Leif Ericson Cruiser
Order of Kilopi
Well, with the same total irradiance, our planet receives only 2% of the Earth's illuminance. But the remainder of the irradiance is coming in as almost entirely UV and shorter wavelengths, as you say. "Terraforming" covers a multitude of options, so we don't know what unlikely measures might be in place to prevent UV getting down to the surface--but much of it is going to be absorbed by an Earthlike atmosphere, and the remainder strongly scattered.
I find it difficult to speculate on what the effect might be, given that we don't know what "terraformed" means in this sort of extreme context.
Grant Hutchison
Order of Kilopi
Okay. I see your argument but I made different assumptions. I’ve thought a bit about possible terraforming techniques, and for a planet too close to a star, I’ve considered filters to reduce the amount of light reaching it, and for planets in orbit around stars with intense UV production, a UV filter would be needed. For hotter stars the filter (possibly a thin disk between the planet and the star) might be made to selectively filter the spectrum to leave something closer to what we receive on Earth (so possibly less blue light as well).
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The Leif Ericson Cruiser
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You want a toroidal cloud in orbit, of tiny particles of a phosphor. Absorb UV and re-radiates as white light. Space launches would only be possible towards the poles.
Order of Kilopi
I think that without additional qualifications, saying the planet is terraformed makes the question unanswerable since there are too many possibilities in what that means in terms of dealing with the star’s light. It could be paraterraformed (essentially a roof across most or all of the planet), a giant disk filter at the planet/star L1 point (assuming that could be stable enough), filters or dust clouds in orbit, or something else.
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The Leif Ericson Cruiser
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It's worth keeping in mind that the habitable zone around an O-type star would be much farther away than for lower-mass, cooler stars like the Sun. Using the O3V star from Grant's comment, by my calculation the habitable zone would start somewhere beyond ~1000-1200 AU. Needless to say the orbital period and seasons on such a planet would last orders of magnitude longer than any human lifetime.
Of all the sciences cultivated by mankind, Astronomy is acknowledged to be, and undoubtedly is, the most sublime, the most interesting, and the most useful. For, by knowledge derived from this science, not only the bulk of the Earth is discovered, but our very faculties are enlarged with the grandeur of the ideas it conveys, our minds exalted above their low contracted prejudices. - James Ferguson
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Also, we wouldn't normally expect to find planets around O-type stars due to the so-called photoevaporation effect that practically kills protoplanetary disks. This effect is understood to be characteristic of O-type and possibly early B-type stars.
Last edited by Fiery Phoenix; 2021-Mar-20 at 04:26 PM.
Of all the sciences cultivated by mankind, Astronomy is acknowledged to be, and undoubtedly is, the most sublime, the most interesting, and the most useful. For, by knowledge derived from this science, not only the bulk of the Earth is discovered, but our very faculties are enlarged with the grandeur of the ideas it conveys, our minds exalted above their low contracted prejudices. - James Ferguson
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And if they do form the life span of the star is just a few million years, not enough time for the crust to cool to anything resembling reasonable temperatures. Sure you could argue that enough "terraforming" could fix that but
by this point that would require pretty much pure magic.
Order of Kilopi
Always, of course, assuming the planet formed with that star.
"I'm planning to live forever. So far, that's working perfectly." Steven Wright
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Yes, of course it goes without saying that there's always the chance of a planet capture. But these stars are rather unlikely to form planets of their own.
Of all the sciences cultivated by mankind, Astronomy is acknowledged to be, and undoubtedly is, the most sublime, the most interesting, and the most useful. For, by knowledge derived from this science, not only the bulk of the Earth is discovered, but our very faculties are enlarged with the grandeur of the ideas it conveys, our minds exalted above their low contracted prejudices. - James Ferguson
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How about a rogue planet drifting close enough to a quasar to terraform (by means that leave the quasar visible). Would the sun-bright quasar twinkle?
SHARKS (crossed out) MONGEESE (sic) WITH FRICKIN' LASER BEAMS ATTACHED TO THEIR HEADS
Order of Kilopi
A quasar would be deadly at naked-eye range, I think.
"I'm planning to live forever. So far, that's working perfectly." Steven Wright
Order of Kilopi
Maybe, maybe not. Quasar power outputs seem to be around 1040W. So for a solar level of irradiance we need to be at about five million AU. For a good night's seeing of two seconds of arc, that's equivalent to a disc diameter of ~50AU, or something like a quarter of a light-day. Quasar accretion disc diameters seem to be measured in multiple light-days. So it would depend on the temperature profile of the disc.
But if you're set on having a twinkling sun illuminating a grotesquely improbable terraformed planet, why not just stick it in orbit around a neutron star? At a million K, 1.4 solar mass and 20km diameter, you can place your planet at 0.43 AU with a period of 0.23 years. It'll receive illumination equivalent to a couple of full moons from a star just 0.06 seconds of arc in apparent diameter. That'll twinkle.
Grant Hutchison
Established Member
Thanks, Grant!
And we know neutron stars at least can have planets (an idea I had a good laugh about with my astronomy professor back in 1976).
SHARKS (crossed out) MONGEESE (sic) WITH FRICKIN' LASER BEAMS ATTACHED TO THEIR HEADS
Established Member
And note that while twinkling has random and variable frequency due to air turbulence, pulsar pulsation has strictly fixed frequency. You can have beat effects between twinkle and pulsar pulsation, especially if both are in same frequency range.
A planet could be illuminated by a Sun-like dwarf and orbit a pulsar. Imagine a planet in a binary of Sun-line dwarf and a pulsar, orbiting the pulsar on a 24 hour orbit - at about 3 million km distance. Tidally locked to the pulsar, and the near side would have 12 hour nights when dwarf is below horizon and pulsar up as always.
How bright would a neutron star at 3 million km be?
Order of Kilopi
You could always put a self repairing sheath held up by a pressurized atmosphere like a bubble. You could not only shield the planet, but have low gravity without worrying about losing air.
Reaching space would require orbital elevators going through fixed openings; it would be complex engineering-wise, but a civilization that can do advanced terraforming described in the OP could handle that.
"I'm planning to live forever. So far, that's working perfectly." Steven Wright
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I'd have to agree; given that, a type O star's lifespan is only 10 million years, it would go supernova before planets really had a chance to form; now, if, say, a rogue planet drifted within the HZ, that's about 1,000AU, yes, but the world would need to be terraformed; it was frozen for eons and, most of the atmosphere should be there, but in a frozen state, converted to gas by drifting near the type-O star.
Now, would it be worth terraforming a rogue planet around an O-class star, know in a few thousand years, the planet would be away from the star and revert back to it's pre-terraformed state?
Order of Kilopi
Well, if it's in a stable orbit it would not break orbit from the primary. Unfortunately for that capture to happen in the first place takes a large body already orbiting the primary for the rogue to interact with. Otherwise the rogue will just come and go. I don't know if a significantly sized object could form in that time to aid in capture.
"I'm planning to live forever. So far, that's working perfectly." Steven Wright
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Yeah, it's very, very, very unlikely that a rogue planet would be captured by a star, unless there were a plethora of rogue-planets out there. So, I am assuming it's just a transiting-planet that happens to be in the HZ and worthy, for some reason, to be terraformed.
Order of Kilopi
I don't know enough orbital mechanics to determine if that's viable or for how long, but certainly the shifting light and heat levels would complicate any efforts. You'd have to work fast, and be prepared to watch it all die off again no matter what.
So, a poor return on investment.
"I'm planning to live forever. So far, that's working perfectly." Steven Wright
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